1. Field of the Invention
The invention relates to a device for optical transmission of data by means of light guides, in which a transmitter and/or a receiver can be moved or differently positioned along a light guide.
Devices of this kind are utilized for example in a linear configuration in crane systems or other conveyor systems for transmitting data between a movable crane and a stationary control unit. Another field of application of these data transmission systems in a circular configuration is a transmission between parts that are rotatable relative to each other, such as, for example, in a computer tomograph between a rotor for supporting an X-ray tube and a detector, and a stationary evaluation unit for processing and displaying image data.
2. Description of the Prior Art
In prior art transmission systems based on light guides, light is coupled into one end of a light guide and then guided through the light guide to the other end thereof where, once again, it is evaluated by a suitable receiver. A multitude of variants, based on this, are known and make possible a simultaneous transmission at a plurality of wavelengths by means of filters, or also a transmission to a plurality of different locations, for example by means of Y couplers. However, systems of this kind are not suitable for coupling signals in or out laterally at arbitrary positions on a light-guiding fiber. For this, various other technologies are known.
A device of this kind is described in U.S. Pat. No. 5,297,225. Here, light coupled in from the outside through notches formed on the outside of the light-guiding medium is deflected by reflections at such angles that it can be guided inside the medium. A transmission device of this kind is expediently usable when coupling-in is to be performed at fixed given positions. Basically it may also be used for a transmission between movable units, because coupling-in or -out of light is performed without contact. However, if a long path of movement is required, as is the case with crane systems or even rotary transmission systems of large diameter, then a very high attenuation results from the many notches along the light-guiding medium. Because of this, extreme demands are made on the dynamic ratio of the receiver. For a path length of several meters, a typical attenuation of this arrangement of about 10 dB per meter overtaxes conventional optical receivers. Therefore, for long transmission paths this transmission system is practicable only with unusually expensive optical components involving large outlay.
Because the technical principles of operation of rotary transmission are the same as those of linear or curved transmission, the following expositions will make no further distinction between them. The terms will be used synonymously. Furthermore, no distinction will be made between the terms light-wave guides and light guides, because their functions are comparable as far as the invention is concerned, although light-wave guides are preferably used in technical practice. Thus, for example, a light guide which is formed substantially by a trench having a mirror surface is suitable for transmitting. A light guide of this kind is disclosed in U.S. Pat. No. 4,525,035.